Fine-grained steels



3,000,731 FINE-GED STEELS Tohei Ototani, Tokyo, Japan, assignor to TheResearch Institute for Iron, Steel and Other Metals of The TohokuUniversity, Sendai City, Japan No Drawing. Filed June 10, 1958, Ser. No.740,995 Claims priority, application Japan Feb. 3, 1958 2 Claims. (Cl.75-129) This invention relates to fine-grained steels and methods ofmanufacturing the same.

The object of this invention is to provide a fine-grained steel havingimproved toughness and machinability.

The control of the grain size of a steel has heretofore been effected byadding to the steel a suitable amount of an element such as Al, Ti, V,Zr and N.

According to this invention, in order to improve grain size control, aFe-Ca base alloy, or other calcium alloys and, if desired, one or moreelements such as cerium, lithium, barium, strontium and magnesium areused.

According to the invention, the iron-calcium base alloy contains 10 to80% iron, 5 to 40% calcium and 5 to 55% of one or more elements selectedfrom the group consisting of nickel, silicon, aluminum and manganese.

The method of this invention is characterized in that a molten bath ofcarbon and alloy steels containing less than about 1.7% of carbon istreated so as to retain 0.001 to 0.05% of calcium by adding theiron-calcium alloy.

An advantage of this invention is that it is not necessary to eifectdeoxidation and de-sulfurization so perfectly that the product containsoxygen from 0.001 to 0.005% and sulfur from 0.003 to 0.015% in order toconstitute finegrained steel. Even when the resulting steel containsmore than 0.015 of sulfur and more than 0.005% of oxygen, it has afine-grained structure provided that the amount of residual calcium inthe product is more than 0.001%.

In carrying out the method of this invention it is necessary for themolten bath to be previously de-oxidized and de-sulfurized suitably.This is desirable for the effective use of the above mentionedadditives.

This invention can be applied to carbon steels and all kinds of alloysteels containing less than 1.7% of carbon, that is, not only to anordinary carbon steel but also to alloy steels containing less than 1.7%carbon together with one or more elements selected from the groupconsisting of silicon, manganese, nickel, cobalt, chromium, copper,aluminum, tungsten, molybdenum, vanadium, titanium and zirconium. Thesteel subjected to the above treatment has fine-grained structure andimproved characteristics without substantial change in tensile strengthand its machinability is improved. The improvement in the mechanicalproperties of such treated steels is remarkable, especially in quenchedand annealed state.

Example I A molten bath of hypo-eutectoid steel containing 0.69%

Patented Sept. 19, 1961 carbon, 0.25% silicon, 1.03% manganese, 0.021%phosphor, 0.022% sulfur was prepared and to this bath was added 0.5% ofFe-Ca base alloy (Fe 15.6%, Mn 12;7%, Ca 20.5%, Si 45.7% and Mg 4.5%.)

A steel ingot manufactured by the above method of this invention afterannealed at 900 C. for 6 hours had a tensile strength of 71.0 kg./mm. anelongation of 25.5% (gauge length, mm.) with a reduction of area of31.6%, and a Brinell hardness number of 177; thus it is characterized inthat the elongation and the reduction of area are high. The ingotcontained a very small amount of non-metallic substances and the grainsize was 7.5 according to the index of Timken A.S.T.M. grain size sothat the steel was finer and cleaner than the grain size 5 of steelwhich is not treated with calcium.

Example 11 A molten bath of chrome molybdenum steel containing 0.35% C,0.19% Si, 0.77% Mn, 1.00% Cr and 0.22% Mo was treated with 1% ofiron-calcium base alloy (Fe 33.5%, Ca 29.5% and Si 36%).

A steel ingot manufactured by the above method of this invention wasquenched and tempered after forging and rolling, and in comparing theresults of the steel which was treated with calcium and that nottreated, the former showed a grain size of 7.9, while the latter showed6.5 A.S.T.M. grain size.

What I claim is:

1. A method of manufacturing a line-grained steel, which comprisesadding to a molten bath of steel containing less than about 1.7 ofcarbon, an iron-calciumsilicon-manganese alloy consisting essentially ofat least 10% of iron, 5 to 40% of calcium and 5 to of manganese andsilicon respectively so as to retain 0.001 to 0.05% of calcium in thecasting, and then casting the molten steel into a mold.

2. A method of manufacturing a fine-grained steel, which comprisesadding to a molten bath of steel containing less than about 1.7 ofcarbon, an iron-calciumsilicon-manganese-aluminum alloy consistingessentially of at least 10% of iron, 5 to 40% of calcium, and 5 to 55%each of manganese, silicon and aluminum, so as to retain 0.001 to 0.05of calcium in the casting, and then casting the molten steel into amold.

References Cited in the file of this patent UNITED STATES PATENTS2,280,283 Crafts Apr. 21, 1942 2,343,956 Crafts Mar. 14, 1944 I FOREIGNPATENTS 885,247 France May 24, 1943 OTHER REFERENCES Carlsson:Jernkontorets Annaler, vol. 137, No. 7, 1948, pages 221-236. Publishedin Stockholm, Sweden.

1. A METHOD OF MANUFACTURING A FINE-GRAINED STEEL, WHICH COMPRISESADDING TO A MOLTEN BATH OF STEEL CONTAINING LESS THAN ABOUT 1.7% OFCARBON, AN IRON-CALCIUMSILICON-MANGANESE ALLOY CONSISTING ESSENTIALLY OFAT LEAST 10% OF IRON, 5 TO 40% OF CALCIUM AND 5 TO 55% OF MANGANESE ANDSILICON RESPECTIVELY SO AS TO RETAIN 0.001 TO 0.05% OF CALCIUM IN THECASTING, AND THEN CASTING THE MOLTEN STEEL INTO A MOLD.